This invention relates to the flow rate regulation of process streams for fluid that is stored in liquid phase and converted to gas phase for use. Regulation is by flow control apparatus situated in the liquid phase that is controlled by a controller sensing conditions of fluid flow in the gas phase. The controller derives the energy from the fluid for its operation and operation of a flow control valve.
It is common practice in industry to store many fluids (which are in gas phase at atmospheric conditions) in liquified form. Such fluids include liquified hydrocarbons like propane, butane and cryogenic gases like argon, oxygen, carbon dioxide, nitrogen, helium and hydrogen. Many liquified gases are maintained at cold temperatures to reduce the need for high storage pressures, such gases being referred to as cryogenic gases. Many liquified gases can be maintained and stored at reasonable pressures not requiring highly reduced temperatures, one such gas being propane. Prior to use of the fluid, the liquified gas is heated and/or has its pressure reduced to convert it from its liquid phase to its gas phase. Such conversion to vapor is accomplished by heating and/or expansion which is typically carried out in a vaporizer or conduit downstream of a valve or can be carried out in an expansion valve alone, or in both. The flow rate of fluid, both in its liquid phase and its gas phase, can be regulated for appropriate flow thru the vaporizer so it is not operated at an over capacity condition and at the point or points of fluid use downstream of the storage tank.
Some such gas supply systems are present for the principal purpose of backup to a primary gas supply system. Such dual systems are commonly found in industries where the gas could be used as a chemical feedstock to a production process (e.g. paper making, petrochemical and chemical refining, mineral extraction, water treatment, etc.) or used as a combustion agent (e.g. steel making, glass making, cement manufacture, non-ferrous metal smelting, etc.) or to control the composition of an atmosphere in a process (e.g. food, glass, metals, electronics, hospitals (for patient use amongst other uses), etc.). Often the continuous supply of gas is critical to life or safety of the process or the prevention of large economic loss-regardless of the presence of energy to operate a control system.
Several forms of flow rate regulating apparatus are used to control fluid flow rate. One device is illustrated in FIG. 1 which utilizes a flow control valve V1 and controller C1 therefor connected in the outfeed conduit OC1 of the vaporizer VP1. The controller receives signals from a temperature sensor TS1 and pressure sensor PS1. The valve and the sensors are situated in the gas phase. Liquified gas is supplied to the vaporizer VP1 from storage tank ST1 via an infeed conduit IC1. One problem with such an arrangement is surging, particularly at lower operating pressures. Another problem with such a system is that the valving required to handle fluid flow when the fluid is in the gas phase are much larger and more expensive than valves used for an equivalent mass flow rate when the fluid is in liquid phase. Such a valve and controller components are available from Kaye and MacDonald a division of Cashco of Elsworth, Kans.
Another such prior art device is illustrated in FIG. 2 where the flow control valve V2 and controller C2 are both positioned in the infeed conduit IC2 connecting the liquified gas storage tank ST2 to a main vaporizer VP2. The main vaporizer is used to provide pressurized fluid in gas phase back to the storage tank thru a conduit CN2 to keep the tank pressurized. The valve is operable to regulate the flow rate of liquified gas therethrough and hence the pressure of the gas phase returning to the tank. A secondary vaporizer VP2xe2x80x2 is connected to the conduit IC2 and the valve to provide a pressure signal to the valve to effect its pressure regulating function. Liquified gas is discharged from the tank for use via an outfeed conduit OC2. Such a system is used solely to control storage tank pressure.
Another arrangement used in the prior art is illustrated in FIG. 3. A storage tank ST3 is connected to a vaporizer VP3 via an infeed conduit IC3. A flow control valve V3 is connected in the infeed conduit IC3 and is controlled by an electronic controller EC3 programmed with operating instructions. The electronic controller receives information from the outfeed conduit OC3 of the vaporizer VP3 sensing properties of the gaseous phase of the fluid with a temperature sensor TS3 and a pressure sensor PS3. Such a system is complex and expensive. Further, its operation requires energy from a remote source which is subject to interruption. Without electrical energy, such a control system may malfunction creating potentially catastrophic results downstream. To overcome such potentialities, backup power systems are provided, such backup systems can include uninterruptable power supplies (UPS), back up generators or both. Such backup energy systems can be quite expensive. A pneumatic control system may also be provided to avoid reliance on power supplies but in the past these have all required an external source of instrument gas to operate the control apparatus.
Thus, there is a need for an improved regulated flow control apparatus for use with fluid systems wherein the fluid is stored as a liquified gas and is used as a vapor.
Among the several objects and features of the present invention may be noted the provision of an apparatus that will regulate the flow rate of fluid from a source of liquified gas to a point of use where the fluid is in vapor phase; the provision of such an apparatus that does not require an external energy source to control the operation of a flow control valve; the provision of such an apparatus where the flow control valve regulates the flow of the liquified gas therethrough; the provision of such an apparatus that monitors conditions of the vapor phase of the fluid downstream to provide information for regulating the flow of the liquid phase; the provision of a method regulating the flow of fluid from a source where it is stored in liquid phase to a point of use where the fluid is used in gas phase; the provision of a method of regulating flow of fluid whereby the fluid flow is regulated at a point where the fluid is in liquid form and the regulation is effected in response to properties of the fluid when in its gas phase downstream of the point of flow regulation; and the provision of an apparatus and method that are economical to implement and effective at flow regulation.
The present invention involves the provision of a system for delivering fluid from a source of liquified gas. The system includes a source storing fluid as liquified gas. A conduit is connected in flow communication with the source and is operable for discharge of fluid from the source. A flow control valve is connected in the conduit flow-wise downstream of the source and separates the conduit into an infeed conduit portion and an outfeed conduit portion with the outfeed conduit portion being flow-wise downstream of the infeed conduit portion. The flow control valve is operable to receive fluid in liquid phase and regulate the flow of fluid in liquid phase from the source to the outlet conduit portion. A controller is operably connected to the flow control valve and operable to control the flow of fluid in liquid phase from the source at least partially thru the flow control valve and to the outfeed conduit portion in response to flow of fluid in its gas phase in the outfeed conduit portion. The controller is substantially completely powered with energy from the fluid in its gas phase.
The present invention further involves the provision of a method of transporting fluid from a source storing the fluid as a liquified gas to at least one point of use where the fluid is in its gas phase. The method includes transporting fluid from a source of fluid in the form of liquified gas to a flow control valve. The flow rate of liquified gas from the source is regulated with the flow control valve, the liquified gas flowing at least partially thru the valve. The fluid is converted from liquified gas to a gas phase downstream of at least a portion of the flow control valve. At least one property of the gas phase is monitored and the flow rate of liquified gas is regulated in response to at least one property of the gas phase. At least a substantial portion of the energy needed to regulate the flow rate of liquified gas from the source is derived from the gas phase of the fluid.
Other objects and features will be in part apparent and in part pointed out hereinafter.